At present intraocular lens made of polymethylmethacrylate are most widely used in ophthalmology.
Intraocular lenses of a polymer material are known (see, e.g., RF patent No. 2074673), which are made by curing a composition prepared from a mixture of oligourethanemethacrylate with the number of oxypropylene groups in the range of from 60 to 150, methylcarbitol methacrylate, methacrylic acid and 2,2-dimethoxy-2-phenylacetophenone, which are taken with the following weight % ratio of the components:
2,2-dimethoxy-2-phenylacetophenone 0.1-0.8 methacrylic acid 2.0-10.0 methylcarbitol methacrylate 20-40 oligourethanemethacrylate balance.
A substantial disadvantage of the polymer material is expressed by the insufficient elasticity of an intraocular lens made therefrom. Intraocular lenses from polymethylmethacrylate feature good optical characteristics and low toxicity. A drawback of these lenses is their high rigidity and hence the possibility of postoperative complications due to injury to surrounding eye tissues.
A method is known for making elastic intraocular lenses by means of high-temperature vulcanization in a casting mold of a silicone-organic polymer with subsequent thermostatic control.
It should be indicated that a prolonged holding of virtually all known polymers at high temperatures around 200-300.degree. C. results not only in their cross-linking, but also to destruction. As a result of polymer destruction, low-molecular products are formed which are capable of diffusing into the eye tissues and causing toxic effects.
Another drawback of this method is that only a very narrow range of materials can be used to make intraocular lenses, i.e. such materials in which the shrinkage factor is close to zero. This also relates to methods for making lens, wherein curing of liquid material in a casting mold occurs under the effect of light or some other radiation. Since the shrinkage factor of the overwhelming majority of light-curable materials lies with the range of from 5 to 22%, it is considered to be impossible to use this method to make lenses having acceptable optical characteristic (see, e.g., "Polymer optic materials," Collection of papers, Chernogolovka, 1989,p. 199).
Known are U.S. Pat. No. 4,382,902 (1983) and No. 4,166,088 (1979), which teach a method for making eye contact lenses by curing a liquid material in a mold made from an optically transparent material under the effect of ultraviolet light. It should be noted that contact lenses are convexo-concave, and a considerable variation in thickness is not characteristic for such lenses. In view of this, it is conceivable that the damping devices provided in casting molds make it possible to attain satisfactory optical characteristics of the lenses.
Since an intraocular lens is biconvex or planoconvex, the variation in thickness is much greater than in contact lenses. Therefore, none of the casting mold constructions makes it possible to produce intraocular lenses having satisfactory optical characteristics, using the aforesaid method.
A method for making an elastic intraocular lens is known, wherein a liquid light-curable material is poured into a casting mold and annealing, i.e. irradiation, is carried out.
The produced intraocular lens also has insufficient elasticity, and this results in increased traumatism of the eye when an operation is performed.
It is often required that an intraocular lens have areas with more and less elasticity. A method for making intraocular lenses is known (see, e.g., RF patent No. 2074673). However, this method does not make it possible to make intraocular lenses having areas with different degrees of elasticity, either.